HTML repr fix for Furo Sphinx theme (#6501)

* Fix for Furo Sphinx theme

* Update `whats-new.rst`

Author: Kevin Paul

doc/whats-new.rst

@@ -87,6 +87,8 @@ Bug fixes
   contain datetime-like values prior to being passed to
   :py:func:`xarray.conventions.decode_cf_variable` (:issue:`6453`,
   :pull:`6489`). By `Spencer Clark <https://github.com/spencerkclark>`_.
+- Dark themes are now properly detected in Furo-themed Sphinx documents (:issue:`6500`, :pull:`6501`).
+  By `Kevin Paul <https://github.com/kmpaul>`_.
 
 Documentation
 ~~~~~~~~~~~~~

xarray/static/css/style.css

@@ -14,6 +14,7 @@
 }
 
 html[theme=dark],
+body[data-theme=dark],
 body.vscode-dark {
   --xr-font-color0: rgba(255, 255, 255, 1);
   --xr-font-color2: rgba(255, 255, 255, 0.54);